core/wire: truncated icmp pkt test

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: ignoramous

intra/core/wire/parsed_test.go

@@ -0,0 +1,63 @@
+// Copyright (c) 2025 RethinkDNS and its authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+// This file incorporates work covered by the following copyright and
+// permission notice:
+//
+//     SPDX-License-Identifier: BSD-3-Clause
+//     Copyright (c) Tailscale Inc & AUTHORS
+
+package wire
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"net/netip"
+	"testing"
+)
+
+func TestParsedDecodeICMPv6EchoRequest(t *testing.T) {
+	// IPv6 ICMP echo request packet (no fragmentation, truncated)
+	hexpkt := "600eb68300403a40fd66f83ac65000000000000000000001260647000000000000000000681084e58000c964116c0002832a586900000000f15b030000000000101112131415161718191a1b1c1d1e1f"
+
+	pkt, err := hex.DecodeString(hexpkt)
+	if err != nil {
+		t.Fatalf("hex decode failed: %v", err)
+	}
+
+	expectedLen := int(binary.BigEndian.Uint16(pkt[4:6])) + IP6HeaderLength
+	if len(pkt) < expectedLen {
+		pkt = append(pkt, make([]byte, expectedLen-len(pkt))...)
+	}
+
+	var p Parsed
+	p.DecodeTrunc(pkt, true)
+
+	if p.IPVersion != Version6 {
+		t.Fatalf("IPVersion got %d, want %d", p.IPVersion, Version6)
+	}
+	if p.IPProto != ICMPv6 {
+		t.Fatalf("IPProto got %v, want %v", p.IPProto, ICMPv6)
+	}
+
+	wantSrc := netip.MustParseAddr("fd66:f83a:c650::1")
+	wantDst := netip.MustParseAddr("2606:4700::6810:84e5")
+
+	if p.Src.Addr() != wantSrc {
+		t.Fatalf("Src got %v, want %v", p.Src.Addr(), wantSrc)
+	}
+	if p.Dst.Addr() != wantDst {
+		t.Fatalf("Dst got %v, want %v", p.Dst.Addr(), wantDst)
+	}
+	if p.Src.Port() != 0 || p.Dst.Port() != 0 {
+		t.Fatalf("expected zero ports for ICMPv6, got src=%d dst=%d", p.Src.Port(), p.Dst.Port())
+	}
+
+	if !p.IsEchoRequest() {
+		t.Fatalf("expected packet to be ICMPv6 echo request")
+	}
+	t.Log(p.ICMPHeaderString())
+}